BRUSSELS (Reuters) - European Union Justice Commissioner Vera Jourova said she had a “constructive and open discussion” with Facebook Chief Operating Officer Sheryl Sandberg about the Cambridge Analytica scandal on Thursday.

The call lasted around half an hour and Jourova said the EU would closely monitor Facebook’s implementation of a strict new EU data protection law which enters into force on May 25.

“Of my particular concern is the information to European citizens affected by the scandal. I was told that Facebook has started to inform people this week,” Jourova said after the call.

Facebook has been hit by revelations that data of some 87 million users were improperly accessed by political consultancy Cambridge Analytica, which worked on U.S. President Donald Trump’s campaign.

“Ms Sandberg also confirmed to me that there could be more apps that harvested personal data of users and those of their friends. I urged Facebook to take all the necessary steps to mitigate any potential negative consequences for the users in the future,” Jourova said.

Sandberg also told Jourova Facebook was working on improving transparency on political advertising.

Jourova said Facebook CEO Mark Zuckerberg should accept the invitation to speak before the European Parliament.

Zuckerberg was questioned for 10 by U.S. lawmakers over the last two days on Facebook’s handling of user data.